In recent years, a low-profile tire has become widely used in response to a request for increasing a speed and lowering a floor level of a vehicle. A tread portion of the low-profile tire is grown in the tire radial direction by applying an internal pressure. Due to the growth in the tire radial direction, there has been concentration of a stress on a groove bottom of a tire circumferential groove and then a crack (a so called groove crack) occurs in the groove bottom.
As a tire to restrain the occurrence of the groove crack, conventionally, there is widely known a tire in which a groove bottom of a circumferential groove is formed in an arc shape and then a curvature radius increases in a cross section taken along a direction orthogonal to an extension direction of a circumferential groove and along a tire radial direction (refer to PTL 1, for example). By increasing the curvature radius of the groove bottom, concentration of a stress on the groove bottom has been restrained. In this manner, the occurrence of the groove crack has been suppressed.